1. Field of the Invention
The present invention relates to multicast packet control apparatuses for use in content information distribution such as broadcasting, and more specifically, to a multicast packet control apparatus for transferring a response report, a join request, and a leave statement.
2. Description of the Related Art
Use of broadband has brought multicast technologies for content distribution such as broadcasting into spotlight. Efficient information distribution can be performed by using a router and an access server supporting IP multicasting for implementing a broadcast service on an Internet Protocol (IP) network built for communication. The Internet Engineering Task Force (IETF) has specified Internet Group Membership Protocol (IGMP) protocols (RFC 1112 and RFC 2236) for IPv4 and a Multicast Listener Discovery (MLD) protocol (RFC 2710) for IPv6, as standard TCP/IP technologies related to multicast communication for distributing data to a plurality of specific destinations. The IGMP and MLD protocols are used between user terminals and a packet transfer apparatus, such as a gateway and a router, and control a user terminal group (multicast group) formed to receive data distributed by multicast distribution for distributing the same data to a plurality of user terminals efficiently. The IGMP and MLD protocols are used when a user terminal makes a join request to a multicast group (a request to distribute multicast data) or sends a leave statement to the multicast group (a request to stop distributing multicast data). When a content distribution server distributes information (a content) as packets, as requested by a user terminal included in a multicast group, in a content distribution service achieved by the technologies related to multicast communication for distributing data to a plurality of specific destinations, a lower packet transfer apparatus (such as a gateway and a router) receives the packet information, makes as many copies of the packet as the user terminals belonging to the requesting multicast group, and transfers the copies to the user terminals.
In a conventional network configuration, when a distribution server sends a join confirmation packet to a plurality of user terminals included in a multicast group, the packet is copied by a Layer 2 switch between the multicast router and the user terminals and sent to the user terminals. The user terminals receive the packet and return a response report packet. In order to prevent congestion on the network because of the response report packets from the user terminals, each user terminal starts a random timer when it receives the join confirmation packet and returns the response report packet when the timer reaches zero. When a first user terminal returns a response report packet, the packet is copied by the Layer 2 switch and can be received by another user terminal in the same subnet. The user terminal receiving the copy recognizes that it does not need to return a response report and will return no response report packet. Therefore, the multicast router can judge whether the multicast data transmission is needed or not by a minimum number of response report packets.
User management such as a multicast accounting service and user approval may not be correctly performed on the network described above. Because the multicast data and the response report packet are copied by the Layer 2 switch and broadcast simultaneously to the user terminals in the same subnet, security is lax.
In recent years, in access networks between user terminals and routers, one physical LAN is divided into a plurality of virtual LANs (VLANs) or the Point-to-Point Protocol over Ethernet (PPPoE) is used. Each of the user terminals and the router are linked in a point-to-point manner, enabling the user to be identified or differentiated and a security check to be run on each user.
[Non-patent document 1]RFC 1112[Non-patent document 2]RFC 2236[Non-patent document 3]RFC 2710